Pass POST parameter to other file

I am having a problem passing a $_POST[] parameter to another file via the URL.
Look at the line 34 and 138.
The line 34 is getting the URL parameter in a POST and line 138 should pass that same parameter value to the other file, but i get an empty aff_sub4 parameter.
EXAMPLE: complete.php?id=38918&aff_sub4=

I don't have a clue why is this happening, because as you can see i am inserting into a database the $name variable and its saved successfully. But when i try to pass it to the other file it gives me empty parameter.
I use JS to pass the $name variable in this code.

<?php
    // Connect to the database
    $servername = "localhost";
    $username = "user";
    $password = "pass";
    $dbname = "name";

    // Create connection
    $conn = mysqli_connect($servername, $username, $password, $dbname);

    // Check connection
    if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
    }

    // Get the user's IP address
    $user_r_ip = $_SERVER['REMOTE_ADDR'];


    function getUserIpAddr(){
        if(!empty($_SERVER['HTTP_CLIENT_IP'])){
            //ip from share internet
            $ip = $_SERVER['HTTP_CLIENT_IP'];
        }elseif(!empty($_SERVER['HTTP_X_FORWARDED_FOR'])){
            //ip pass from proxy
            $ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
        }else{
            $ip = $_SERVER['REMOTE_ADDR'];
        }
        return $ip;
    }

    // Get the URL parameters
    $name = $_POST['name'];
    $amount = $_POST['amount'];

    //Get User Location details
    $user_ip = getUserIpAddr();
    $geo = unserialize(file_get_contents("http://www.geoplugin.net/php.gp?ip=$user_ip"));
    $country = $geo["geoplugin_countryName"];

    if ($_SERVER['REQUEST_METHOD'] == 'POST' && isset($_POST['name']) && isset($_POST['amount'])) {
      // Prepare the INSERT statement
      $stmt = mysqli_prepare($conn, "INSERT INTO names (name, amount, country, ip) VALUES (?, ?, ?, ?)");

      // Bind the parameters
      mysqli_stmt_bind_param($stmt, "ssss", $name, $amount, $country, $user_r_ip);

      // Execute the statement
      if (!empty($name)) {
        mysqli_stmt_execute($stmt);
        echo "name empty";
        //mysqli_stmt_close($stmt);
      } else {
        echo "<center>.</center>";
        mysqli_close($conn);
        $conn-exit();
      }
    }

?>
<?php

    // Setup Variables
    $api_key = 'my_api_key'; // Enter the API key that you have generated on our main Offer API page

    $endpoint = 'https://downloadlocked.com/api/v2'; // The endpoint show in our main Offer API page

    $data = [
        'ip' => $_SERVER['REMOTE_ADDR'], // Client IP (REQUIRED)
        'user_agent' => $_SERVER['HTTP_USER_AGENT'], // Client User Agent (REQUIRED)
        'ctype' => 7,
        'max' => 25,
        'min' => 6
        // Enter other optional vars here (ctype, max, etc)
    ];

    // Create URL
    $url = $endpoint . '?' . http_build_query($data);

    // Start CURL
    $ch = curl_init();

    // Set CURL options
    curl_setopt_array($ch, [
        CURLOPT_URL            => $url,
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_HTTPHEADER     => [
            'Authorization: Bearer ' . $api_key,
        ],
    ]);

    // Execute request
    $content = curl_exec($ch);

    // Check for error
    if ($content === false) {
        // Throw exception if request failed
        throw new Exception(curl_error($ch));
    }

    // Close CURL
    curl_close($ch);

    // Parse JSON response
    $content = json_decode($content, null, 512, JSON_THROW_ON_ERROR);

    if($content->success) {

        // If API response reported an success...
        $offers = $content->offers; // Do something with $offers


        usort($offers, function($a, $b) {
            return $b->payout <=> $a->payout;
        });


    } else {
        // If API response reported an error...
        throw new Exception($content->error);
    }
?>

<body>

    <h3>Confirm Firewall & User-Agent</h3>
    <p class="desc">Complete 2 offers</p>
    <p class="desc"><b>USING VPN WILL NEVER CONFIRM SUCCESSFULLY THE FIREWALL</b></p>
    <div class="offer-container">
        <?php
        foreach ($offers as $offer) {
          // Extract the image URL, short name, and ad copy from the offer object
          $imageUrl = $offer->picture;
          $nameShort = $offer->name_short;
          $adCopy = $offer->adcopy;
          $offerid = $offer->offerid;
          $adLink = $offer->link."&aff_sub4=".$name;

          ?>

          <div class="offer">
              <img src="<?= $imageUrl ?>" alt="<?=$nameShort?>">
              <div>
                <h3><a href="complete.php?id=<?=$offerid?>"><?=$nameShort?></a></h3>

                <p><?=$adCopy?></p>
              </div>
          </div>

          <?php
        }
        ?>
    </div>
</body>
</html>

I have no errors to show you because i dont get any errors.